Grounding and ground fault detection circuits

Abstract

In an AC electric power system including a voltage source having a live conductor and a neutral, a grounding and ground fault detection circuit connected between the neutral and ground potential and comprising, in series, a current limiter, a rectifier, and a signal generator for providing a control signal in response to a ground fault current.

The invention claimed is: 
     
       1. In an AC electric power distribution system including an AC voltage source having a pair of terminals respectively corresponding to service voltage and neutral with a voltage applied therebetween, the service voltage terminal being at a potential to ground on the order of the applied voltage, a grounding and ground fault detection circuit connected between neutral and ground and comprising, in series, current limiting means, AC blocking means for preventing capacitive leakage current flow between ground and neutral through said circuit and for permitting DC current flow between ground and neutral through said circuit in the event of a ground fault, and means for generating a control signal in response to said DC current flow. 
     
     
       2. The invention of claim 1, wherein said voltage source includes a transformer. 
     
     
       3. The invention of claim 1, wherein said grounding and ground fault detection circuit includes, in series with said current limiting means, AC blocking means, and control signal generating means, a DC power supply for generating a DC current through said circuit in the event of a fault between neutral and ground. 
     
     
       4. The invention of claim 1, wherein said control signal generating means comprises light emitting means. 
     
     
       5. The invention of claim 1, wherein said AC blocking means is a half-wave rectifier. 
     
     
       6. The invention of claim 1, wherein said current limiting means comprises a resistance. 
     
     
       7. A grounding and ground fault detection system comprising, in combination, a transformer and a grounding and ground fault detection circuit, the transformer including a secondary winding having a pair of connection points respectively corresponding to service voltage and neutral with a voltage applied therebetween, the service voltage connection point being at a potential to ground on the order of said applied voltage, the grounding and ground fault detection circuit being connected between neutral and ground and including, in series, current limiting means, AC blocking means for preventing capacitive leakage current flow between ground and neutral through said circuit and for permitting DC current flow between ground and neutral through said circuit in the event of a ground fault, and means for generating a control signal in response to said DC current flow. 
     
     
       8. A system in accordance with claim 7, wherein said grounding and ground fault detection circuit further includes, in series with said current limiting means, AC blocking means, and control signal generating means, a DC power supply for generating DC current through said circuit in the event of a fault between neutral and ground. 
     
     
       9. A system in accordance with claim 7, wherein said transformer is a three-phase transformer with a wye-connected secondary. 
     
     
       10. A system in accordance with claim 7, wherein said AC blocking means is a half-wave rectifier. 
     
     
       11. A system in accordance with claim 7, wherein said current limiting means comprises a resistance. 
     
     
       12. A system in accordance with claim 7, wherein said control signal generating means comprises light emitting means. 
     
     
       13. A system in accordance with claim 12, wherein said grounding and ground fault detection circuit includes means for protecting said light emitting means.